PHILADELPHIA — Human diversity in Africa is greater than any place else on Earth. Differing food sources, geographies, diseases and climates offered many targets for natural selection to exert powerful forces on Africans to change and adapt to their local environments. The individuals who adapted best were the most likely to reproduce and pass on their genomes to the generations who followed.

Sarah Tishkoff measures the height of a Sandawe man.

A member of the Hadza tribe of Tanzania, a young boy practices his archery skills.